A report by a UN expert urges the US to ‘release its own data on the level of civilian casualties’ caused by drone strikes and attacks the lack of transparency surrounding CIA and US special forces drone operations.

Ben Emmerson, a British barrister and UN special rapporteur on counter-terrorism, has released the second of two major UN reports in a week to examine the use of drones both in conflict zones and in covert settings.

In the earlier report, Christof Heyns also called for increased transparency around the use of drones. In the new report Emmerson emphasises that this is a vital step to ensuring accountability and redress for the civilian victims of drone strikes.

‘The Special Rapporteur does not accept that considerations of national security justify withholding statistical and basic methodological data’– Ben Emmerson

Emmerson says: ‘The single greatest obstacle to an evaluation of the civilian impact of drone strikes is lack of transparency, which makes it extremely difficult to assess claims of precision targeting objectively.’

The report says the involvement of the CIA in drone operations has created an ‘almost insurmountable obstacle to transparency’, and he is also critical of the ‘almost invariably classified’ nature of special forces drone operations in Yemen and Somalia. ‘The Special Rapporteur does not accept that considerations of national security justify withholding statistical and basic methodological data.’

Drones currently operate in an ‘accountability vacuum’, Emmerson says, adding that there is a legal obligation on states to launch a full investigation into claims from ‘any plausible source’ of civilian casualties – including those made by non-governmental organisations. The results of such investigations should be made public, ‘subject to redactions on grounds of national security’, he adds.

He notes that the current director of the CIA John Brennan has called for the release of data relating to civilian casualties. The US government is in the process of moving its drone operations from the CIA to the Department of Defense to improve transparency, he says, adding that he understands this is due to be completed ‘by the end of 2014′.

The report highlights ‘differences of view’ over who should be considered a civilian in situations where non-uniformed fighters live and operate among the civilian population. He points to ‘considerable uncertainty’ over the criteria used to identify individuals as legitimate targets and calls for further clarification.

‘Only in the most exceptional of circumstances would it be permissible under international human rights law for killing to be the sole or primary objective of an operation’– Ben Emmerson

The Pakistani government released data to Emmerson showing at least 400 civilian casualties – a number close to the Bureau’s lower-end estimate – and a further 200 were ‘regarded as probable non-combatants’. Emmerson wrote ‘those figures were likely to be an underestimate’ according to local officials. He told MSNBC there is no reason ‘on the face of it’ to question this data as it echoed independent estimates.

For Yemen drone operations, the report cites the Bureau’s estimate of 21-58 civilian casualties as the highest such figures. But the report does not provide estimates for drone operations in Afghanistan, Libya, Iraq, Somalia or Gaza, pointing to a lack of official figures specifically covering civilians killed in drone strikes.

Kat Craig, Legal Director of the human rights charity Reprieve, which represents civilian victims of drone strikes, said: ‘This report highlights the US’ failure to reveal any information whatsoever about their shadowy, covert drone programme. Hiding the reality of civilian deaths is not only morally abhorrent but an affront to the sort of transparency that should be the hallmark of any democratic government. Some basic accountability is the very least people in Pakistan and Yemen should expect from the CIA as it rains down Hellfire missiles on their homes and villages.’

Emmerson also addresses the legality of drone strikes outside of military conflict areas, saying that where no official conflict exists lethal action will ‘rarely be lawful… because only in the most exceptional of circumstances would it be permissible under international human rights law for killing to be the sole or primary objective of an operation’.

The US claims it can legally carry out such lethal operations – but Emmerson says this ‘gives rise to a number of issues on which there is either no clear international consensus, or United States policy appears to challenge established norms’. The US has claimed that it carries out drone strikes in countries including Pakistan and Yemen in legitimate self-defence against imminent threats and that it is in a state of continuing war against al Qaeda and associated groups.

The report recommends that a clear international legal consensus is reached and Emmerson is currently consulting states with a view to ‘clarifying their position on these questions’.

He writes that he has identified 33 strikes that appear to have led to civilian casualties and ‘undoubtedly raise issues of accountability and transparency’. The full findings on these strikes will be published at a later stage.

A White House spokeswoman, Laura Magnuson, said: ‘We are aware that this report has been released and are reviewing it carefully.’

The reports by Heyns and Emmerson will be presented to the UN General Assembly in New York next week. Also next week on October 22 Amnesty International and Human Rights Watch will publish reports on drone operations in Pakistan and Yemen respectively.